1. Field of the Invention
The present invention relates to a power supply device for driving a motor, which is mounted on a vehicle having a motor for making the vehicle travel and, more particularly, to a power supply device for a vehicle, for efficiently controlling temperature of a battery included in the power supply device.
2. Description of the Related Art
Vehicles such as an electric vehicle and a hybrid vehicle are used in extremely hostile temperature environment. In summer, a vehicle is exposed to the scorching sun and the temperature becomes extremely high. In the middle of winter or the like, the temperature becomes extremely low. When the temperature is high and low, the electric performance of a power supply device built in a vehicle used in the environment deteriorates. Specifically, when the temperature is low, the dischargeable capacity of a battery included in the power supply device decreases. On the other hand, when the temperature is high, the self discharge increases and the remaining capacity decreases. To prevent such a problem, a heat exchanger for cooling and heating the battery is provided and the temperature of the battery is controlled to be in a predetermined temperature range.
When a heat exchanger dedicated to a battery is provided to perform temperature control, however, the energy is consumed by the amount corresponding to the temperature control, and the use efficiency of the battery deteriorates. Consequently, a mechanism in which an air conditioner unit for adjusting the temperature in a vehicle is used for adjusting battery temperature has been developed (Japanese Patent Publication Laid-open No. Hei 7-73906). With the configuration, cold air from the air conditioner for cooling the room is used also for cooling the battery. However, the output of the air conditioner is consumed, not only for cooling the room, but also for cooling the battery, so that general power consumption of the air conditioner increases and the energy is consumed.
The applicant of the present invention has developed a power supply device for a vehicle (Japanese Patent Publication Laid-open No. 2003-203679), in which the temperature of the outside air is detected in a state where an ignition switch is off. Only when the temperature of the outside air is out of a set temperature range, a temperature control circuit determines a temperature control mode in which a battery unit is subjected to temperature control. An input circuit selects the temperature control mode of controlling the temperature of the battery unit, and the temperature of the battery unit is controlled by a heat insulating mechanism. On the other hand, when the input circuit selects a state in which the battery unit is not set in the temperature control mode even if the outside air temperature lies out of the set temperature range, the battery unit is not subjected to the temperature control. With this configuration, the user determines finally and executes the temperature control on the battery unit. Consequently, while suppressing excessive battery consumption, the battery can be protected from the high and low temperatures even in the state in which the ignition switch is off. However, in this configuration as well, the power of the power supply device is consumed for controlling the temperature of the battery, so that the energy efficiency is low. Consequently, a technique capable of improving the use efficiency of the battery by further suppressing power consumption is in demand.